1) Field of the Invention
The present invention relates to an image forming apparatus having a structure of a multi function product that includes all or at least two of the functions of an electronic copying machine, a printer, and a facsimile machine.
2) Description of the Related Art
Conventionally, an image forming apparatus using an intermediate transfer method is well known in which a toner image formed on an image carrier is transferred to an intermediate transferring body, and the toner image transferred to the intermediate transferring body is bulk transferred to a recording medium. In such type of the image forming apparatus, photosensitive drums, for example, are used as an image carrier with toner images formed thereon according to the image data, and an endless intermediate transfer belt stretched over a plurality of rollers is used, for example, as the intermediate transferring body. A transfer electric field formed between the photosensitive drum and the intermediate transfer belt during a primary transfer is used as a primary transfer unit that transfers the toner image of the photosensitive drum to the intermediate transfer belt, and a transfer electric field formed between the intermediate transfer belt and a transfer material is used as a secondary transfer unit that transfers the toner image of the intermediate transfer belt to the recording medium. The primary transfer unit needs to precisely and stably transfer the toner image formed on the photosensitive drum to the intermediate transferring body. Similarly, the secondary transfer unit also needs to precisely and stably transfer the toner image formed on the intermediate transferring body to the recording medium. In other words, a stable transfer with high transfer efficiency needs to be carried out to realize the performance of the primary and the secondary transfer units.
In the image forming apparatus that uses the intermediate transfer method, it is extremely difficult to attain a hundred percent transfer efficiency when the toner image is transferred to the recording medium by the secondary transfer unit, and after the secondary transfer, a part of the toner image invariably remains on the intermediate transfer belt, necessitating the inclusion of a belt cleaning device in the intermediate transfer belt. Cleaning blades are widely used as a belt cleaning device.
However, in such type of the belt cleaning device, curling or choking of the cleaning blade present obstacles for development. The technology of supplying a lubricant to the belt that is to be cleaned is widely known and is disclosed, for example, in Japanese Patent Laid-Open Publication No. S57-17973, Japanese Patent Laid-Open Publication No. H7-271142, and Japanese Patent Laid-Open Publication No. 2001-75449, to overcome this drawback.
However, since supplying a lubricant on the intermediate transfer belt reduces the surface friction coefficient of the belt, if the surface friction coefficient of the belt becomes too low as compared to the friction coefficient of the photosensitive drum surface, the primary transferability deteriorates, thereby causing image defects such as omission of image during transfer.